On the other hand, more recent studied found no differences in the statistical properties of FGs and non-FGs samples [1]}, [2]}, [3]}. In particular, these authors claimed that it is crucial to use homogeneous data and procedures to analyse both the FG and the control samples. According to their statements, this could be the source of the excess of X-ray luminosity (or the lack of optical luminosity) found in the previous studies.
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